1. Field of the Invention
The present invention relates, generally, to a method for preparing a PtCo nanocube catalyst by dissolving a platinum (Pt) precursor, a cobalt (Co) precursor, a surface stabilizer and a reducing agent in a solvent and heating the mixture to prepare PtCo nanocubes, adsorbing them on a carbon support, and then removing the surface stabilizer. The PtCo nanocube catalyst prepared in accordance with certain preferred embodiments of the present invention may be useful in the development of high-efficiency fuel cells.
2. Background Art
With concerns about the depletion of fossil fuel, research and interest on next-generation energy sources have been increasing worldwide. Accordingly, hydrogen fuel cells have been studied in academic circles and industries as an environmentally-friendly energy source that does not emit pollutants. In particular, hydrogen fuel cells are expected to replace the existing petroleum-based engine in automobiles and are drawing considerable attention in the alternative energy market.
A proton exchange membrane fuel cell (PEMFC) is a system which transforms the chemical energy liberated during the electrochemical reaction of hydrogen and oxygen to electrical energy. Hydrogen is oxidized at the anode, and oxygen is reduced at the cathode, thereby producing water. It is an environmentally-friendly energy source that does not produce any pollutants. The operation temperature is relatively low at 50-100° C. and energy density is high. For these reasons, it may be used as small-scale energy source for household use as well as car engines. However, there are problems to be solved, including low output energy density due to low reaction rate, use of a large amount of platinum (Pt) catalyst, and removal of water vapor formed on the electrode surface.
Present research has focused on addressing these problems and commercializing the PEMFC. In particular, improving cell efficiency through improvement of fuel cell catalyst is considered to be of great importance.
For the metal catalyst used for reduction of oxygen, it is known that alloys of Pt and various transition metals exhibit superior catalytic activity to pure Pt catalyst. Especially, PtCo alloy is reported to show about 3 times better activity (J. K. Norskov, et al. Angew. Chem. Int. Ed., vol. 45, p. 2897). Also, it is known that cubic Pt catalyst with crystal planes exhibits better activity than spherical Pt catalyst. Accordingly, in order to suitably improve activity, the metal catalyst is preferably a cubic PtCo alloy with uniform particle size and narrow particle size distribution and be adsorbable on a carbon support.
Recently, nanocolloid synthesis has been the focus of research because it enables the easy preparation of such a metal catalyst. Nanocolloids are advantageous in that they can be suitably arranged without agglomeration because of the surfactant acting as a surface stabilizer. In addition, a high catalytic activity may be suitably attained because loading of the nanocolloids is possible with a relatively small quantity. Consequently, nanocolloids are highly promising since they enable high metal loading and preparation of nano-scale metal alloy with uniform size. Nanocolloid synthesis is advantageous in that uniform interparticle spacing can be suitably achieved by preventing agglomeration or coalescence of nanocolloid particles, alloying with two or more metals is suitably possible since the colloidal structure enables easy control of metal composition by varying the equivalence of metal salt during the synthesis, and uniform size, narrow size distribution and high metal loading can be suitably achieved. However, in order to achieve high catalytic activity, it is necessary to remove the surface stabilizer from the obtained nanocolloid.
Korean Patent No. 10-0823502, Japanese Patent Application Publication No. 2003-045442 and US Patent Application Publication No. 2009-0104497, incorporated by reference in their entireties herein, disclose preparation of Pt alloy catalysts, including PtCo; however the methods are not appropriate for industrial-scale production of catalyst because they require high-temperature heat treatment.
Accordingly, methods for improving catalytic activity are needed in the art.
The above information disclosed in this the Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.